Electromagnetic relay circuits



w. H. SCHEER 2,034,881

Min-ch24, 1936.

ELECTROMAGNETIC RELAY CIRCUITS Filed May 26, 1 933 F/G.2 3 f lg f1 2 l lE j I T 1 5 2 7 F/G.4 i .LM w I T INVENTOR WHSCHEER" A TTORNE Y PatentedMar. 24, 19 36 UNITED STATES PATENT OFFICE William H. Scheer, Montclair,N. Bell Telephone Laboratories, New York, N. Y., a corporation ofApplication May 26,

2 Claims.

This invention relates to relay circuits and more particularly to meansfor operating relays where a variety of circuit conditions areencountered. 4

An object of the invention is to operate a relay in a uniform mannerunder various conditions of applied potential and circuit resistance.

Another object is to keep the magnetic flux in a relay substantiallyconstant over a predetermined range of applied potentials.

An additional object is to operate a relay on a predetermined range ofapplied potentials and to render it inoperative on potentialsoutside'said range.

Still another object is to make the operating time of a relay uniformover a range of energizing potentials.

A feature of the present invention whereby the above stated objects areattained, resides in connecting a secondary winding on the relay inopposition to the energizing winding and in connecting a resistanceelement in series with said secondary winding, said resistance elementhaving the characteristic of decreasing in resistance substantiallyinstantaneously with an increase in applied potential.

The invention will be understood from the following description,together with the accompanying figures of the drawing in which theinvention is illustrated:

Fig. 1 shows my invention applied to an electromagnetic relay circuit;

Fig. 2 is a curve illustrating certain relay characteristics obtainablein a circuit arranged according to my invention; 1

Fig. 3 is a curve illustrating other characteristics obtainable in acircuit arranged according to my invention;

Fig. 4 shows my invention applied to a slow acting relay circuit; and

Fig. 5 is a curve illustrating certain time characteristics of thisrelay.

In Fig. 1, 3 is an electromagnetic relay having two windings l and 2 sowound thereon that when they are connected in parallel circuits asshown, the currents through winding 2 tend to set up a magnetic field inthe relay core of opposite polarity to that set up by the currents inwinding I. This is indicated in the drawing by the two oppositelydirected arrows. Hence, the total magnetic flux in the relay core willbe the difference between that which would be caused by winding 1 andthat which would be caused by winding 2 it energized independently.

windings I and 2 are in parallel circuits both J., assignor toIncorporated.

New York 1933, Serial No. 672,983

of which are connected in series with a source of electric current 5and, for purposes of illustration, a resistance 6. In the parallelbranch of the circuit which includes winding 2 is also connected aresistance element 4 which has the characteristic of substantiallyinstantaneously decreasing its resistance to current flow with anincrease in the potential difference applied across its terminals. Suchan element may be the synthetic resistance material described andclaimed in U. S. Patent 1,822,742 or it may be any other element knownto the art which is of like characteristics.

By making windings i and 2 of relay 3 of certain desired resistancevalues and designing nonohmlc resistance element 4 to have the desiredresistance-voltage characteristics a circuit may be obtained whereinrelay 3 will have substantially the same flux (and hence will attractits armature with the same force) for a wide variety of applied voltagesand circuit resistances. This is illustrated in the curve of Fig. 2which shows the relation between the flux and the voltage (E) applied tothe relay circuit. This voltage will depend, for example, on thepotential of source 5 and the value of resistance 6. The current inwinding i will be directly proportional to the voltage while that inwinding 2 will increase with voltage in greater than direct proportion.Thus,

v with increase of applied voltage, the effects of the I current inwinding 2 will cancel progressively greater proportions of the effectsof the current in winding I.

On the curve )1 is a horizontal line representing the minimum fluxnecessary to operate the relay. The solid line curve shows the flux inthe relay for various voltages. It will be noticed that the fluxincreases with voltage to a certain point after which it remainssubstantially constant at a value indicated as in.

A relay circuit having the above characteristics is of value, forexample, where awide variety of circuit conditions are encountered anduniform relay operation is required. Such is the case, for example, intelephone systems having pulsing relay circuits where a relay at acentral oiilce is required to operate and release in responseto dialpulses from a subscribers station. Such subscribers are located atvarious distances from the central ofllce a wide variety of lineresistances are encountered and hence different potentials are appliedto the pulsing relays.

Fig. 3 shows a curve for a relay circuit in which, by the selection of aresistance element which has the proper voltage-resistancecharacteristic and byproperly proporticnlng the turns tacts, currentstarts to build up in windings i and the relay'shall have insufilcientflux to operate,

or-to hold operated, it is only necessary to so proportion the windingsl and 2 of Fig. 1 and to choose an element i having such avoltageresistance characteristic that applied potentials higher than thepredetermined maximum will cause such a lowering of the resistance ofelement and a consequent increase in the flux caused by winding 2 thatthe flux difierence between windings l and 2 will be carried below thevalue necessary to hold the relay operated, hence it will release.

Fig. 4 shows a circuit slow-to-operate characteristics. might beproduced, for example, by attaching a copper sleeve or collar around oneend of the relay core.

When key I is in which relay 3 has depressed, thus closing its con- 2 ofrelay 3 thus building up the flux in the core until it reaches theoperating point of the relay. This is illustrated in Fig. 5 by the solidcurve which shows the relation between flux and time measured from theclosure of the contacts of key 1. The operating time of the relay willthen be h. With a circuit including a non-ohmic resistance element suchas i, the operating time can be made to be a constant for a wide rangeof energizing potentials. The value of the op erating time of a relaymay be expressed in a formula as follows: i

' t=K log m Such a relay.

and h is the flux required to operate the relay. Since ii is a constantfor the the same value for a variety of energizing voltages it followsthat t will be a constant (equal to t1) regardless of voltage, within acertain range.

In a relay circuit not arranged according to my invention, aihigherenergizing potential will cause quicker operation of the relay asindicated by the dash line curve (Fig. 5). In this case, the op-'erating-time of the relay with a certain high energizing potential willbe 152 and with a cer= tain lower energizing potential it will be M.

An actual relay connected in a circuit arranged according to myinvention operated in from .054 to .064 seconds when various potentialsranging from 20 to 45 volts were applied. The same relay with winding 2disconnected showed an operating time of .070 seconds with the fluxadjusted to is at 20 volts and only .020 seconds at 45 volts.

While. the invention has been shown and described as embodied in certainspecific arrange-- constant at any applied voltage above a predeterminedvalue comprising a relay, two opposing windings therefor connected inparallel and a resistance element in series with one of said windings,said element having the characteristic of decreasing in resistancesubstantially instantaneously with an increase of applied potential.

H. SCI-IEER.

relay and is has

